The radio galaxy 0402+379 is believed to host a supermassive black hole binary (SMBHB). The two compact core sources are separated by a projected distance of 7.3 pc, making it the most (spatially) compact resolved SMBHB known. We present new multi-frequency VLBI observations of 0402+379 at 5, 8, 15 and 22 GHz, and combine with previous observations spanning 12 years. A strong frequency dependent core shift is evident, which we use to infer magnetic fields near the jet base. After correcting for these shifts we detect significant relative motion of the two cores at β = v/c = 0.0054 ± 0.0003 at P A = −34.4 • . With some assumptions about the orbit, we use this measurement to constrain the orbital period P ≈ 3 × 10 4 y and SMBHB mass M ≈ 15 × 10 9 M . While additional observations are needed to confirm this motion and obtain a precise orbit, this is apparently the first black hole system resolved as a visual binary.

We present the detection of a bright radio burst at radio frequencies between 2.2-2.3 GHz with the NASA Deep Space Network (DSN) 70 m dish (DSS-63) in Madrid, Spain from FRB 20200120E. This repeating fast radio burst (FRB) was recently discovered by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) instrument and reported to be associated with the M81 spiral galaxy at a distance of 3.6 Mpc. The high time resolution capabilities of the recording system used in this observation, together with the small amount of scattering and intrinsic brightness of the burst, allow us to explore the burst structure in unprecedented detail. We find that the burst has a duration of roughly 30 µs and is comprised of several narrow components with typical separations of 2-3 µs. The narrowest component has a width of 100 ns, which corresponds to a light travel time size as small as 30 m, the smallest associated with an FRB to date. The peak flux density of the narrowest burst component is 270 Jy. We estimate the total spectral luminosity of the narrowest component of the burst to be 4 × 10 30 erg s -1 Hz -1 , which is a factor of ∼500 above the luminosities of the so-called "nanoshots" associated with giant pulses from the Crab pulsar. This spectral luminosity is also higher than that of the radio bursts detected from the Galactic magnetar SGR 1935+2154 during its outburst in April 2020, but it falls on the low-end of the currently measured luminosity distribution of extragalatic FRBs. These results provide further support for the presence of a continuum of FRB burst luminosities. Subject headings: fast radio burst: individual (FRB 20200120E)

Interstellar scattering causes pulsar profiles to grow asymmetrically, thus affecting the pulsar timing residuals, and is strongest at lower frequencies. Different Interstellar medium models predict different frequency (ν) and dispersion measure (DM) dependencies for the scattering time-scale τ sc . For Gaussian inhomogeneity the expected scaling relation is τ sc ∝ ν −4 DM 2 , while for a Kolmogorov distribution of irregularities, the expected relation is τ sc ∝ ν −4.4 DM 2.2 . Previous scattering studies show a wide range of scattering index across all ranges of DM. A scattering index below 4 is believed to be either due to limitations of the underlying assumptions of the thin screen model or an anisotropic scattering mechanism. We present a study of scattering for seven nearby pulsars (DM < 50 pc cm −3 ) observed at low frequencies (10 − 88 MHz), using the first station of the Long Wavelength Array (LWA1). We examine the scattering spectral index and DM variation over a period of about three years. The results yield insights into the small-scale structure of ISM as well as the applicability of the thin screen model for low DM pulsars.Assuming that the scattering occurs due to a thin screen between the observer and the source, the pulse broadening function can be expressed in terms of an exponential function ∼ exp(−t/τ sc ) with scattering parameter τ sc (Scheuer 1968). This is also known as the thin-screen model where different ISM models of electron density fluctuations predict different frequency dependencies for the scattering parameter given by τ sc ∝ ν −α , where α is the scattering time spectral index.

We report on NICER X-ray monitoring of the magnetar SGR 1830−0645 covering 223 days following its 2020 October outburst, as well as Chandra and radio observations. We present the most accurate spin ephemerides of the source so far: ν = 0.096008680(2) Hz, ν ̇ = − 6.2 ( 1 ) × 10 − 14 Hz s−1, and significant second and third frequency derivative terms indicative of nonnegligible timing noise. The phase-averaged 0.8–7 keV spectrum is well fit with a double-blackbody (BB) model throughout the campaign. The BB temperatures remain constant at 0.46 and 1.2 keV. The areas and flux of each component decreased by a factor of 6, initially through a steep decay trend lasting about 46 days, followed by a shallow long-term one. The pulse shape in the same energy range is initially complex, exhibiting three distinct peaks, yet with clear continuous evolution throughout the outburst toward a simpler, single-pulse shape. The rms pulsed fraction is high and increases from about 40% to 50%. We find no dependence of pulse shape or fraction on energy. These results suggest that multiple hot spots, possibly possessing temperature gradients, emerged at outburst onset and shrank as the outburst decayed. We detect 84 faint bursts with NICER, having a strong preference for occurring close to the surface emission pulse maximum—the first time this phenomenon is detected in such a large burst sample. This likely implies a very low altitude for the burst emission region and a triggering mechanism connected to the surface active zone. Finally, our radio observations at several epochs and multiple frequencies reveal no evidence of pulsed or burst-like radio emission.

PSR B1508+55 is known to have a single component profile above 300 MHz. However, when we study it at frequencies below 100 MHz using the first station of the Long Wavelength Array, it shows multiple components. These include the main pulse, a precursor, a postcursor, and a trailing component. The separation of the trailing component from the main peak evolves over the course of a three year study. This evolution is likely an effect of the pulse signal getting refracted off an ionized gas cloud (acting as a lens) leading to what appears to be a trailing component in the profile as the pulsar signal traverses the interstellar medium. Using this interpretation, we identify the location and electron density of the lens affecting the pulse profile.